linux-kernel - [PATCH 20/36] rust: sync: atomic: Add atomic bool support via i8 representation

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Message-ID: <20260111120209.6133-18-boqun.feng@gmail.com>
Date: Sun, 11 Jan 2026 20:01:53 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: "Peter Zijlstra" <peterz@...radead.org>,
	"Ingo Molnar" <mingo@...nel.org>
Cc: rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Will Deacon" <will@...nel.org>,
	"Mark Rutland" <mark.rutland@....com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Miguel Ojeda" <ojeda@...nel.org>,
	"Gary Guo" <gary@...yguo.net>,
	"Alice Ryhl" <aliceryhl@...gle.com>,
	"Andreas Hindborg" <a.hindborg@...nel.org>,
	"Benno Lossin" <lossin@...nel.org>,
	"Danilo Krummrich" <dakr@...nel.org>,
	FUJITA Tomonori <fujita.tomonori@...il.com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [PATCH 20/36] rust: sync: atomic: Add atomic bool support via i8 representation

From: FUJITA Tomonori <fujita.tomonori@...il.com>

Add `bool` support, `Atomic<bool>` by using `i8` as its underlying
representation.

Rust specifies that `bool` has size 1 and alignment 1 [1], so it
matches `i8` on layout; keep `static_assert!()` checks to enforce this
assumption at build time.

[boqun: Remove the unnecessary impl AtomicImpl for bool]

Link: https://doc.rust-lang.org/reference/types/boolean.html [1]
Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Link: https://patch.msgid.link/20260101034922.2020334-2-fujita.tomonori@gmail.com
---
 rust/kernel/sync/atomic/predefine.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs
index 248d26555ccf..3fc99174b086 100644
--- a/rust/kernel/sync/atomic/predefine.rs
+++ b/rust/kernel/sync/atomic/predefine.rs
@@ -5,6 +5,17 @@
 use crate::static_assert;
 use core::mem::{align_of, size_of};
 
+// Ensure size and alignment requirements are checked.
+static_assert!(size_of::<bool>() == size_of::<i8>());
+static_assert!(align_of::<bool>() == align_of::<i8>());
+
+// SAFETY: `bool` has the same size and alignment as `i8`, and Rust guarantees that `bool` has
+// only two valid bit patterns: 0 (false) and 1 (true). Those are valid `i8` values, so `bool` is
+// round-trip transmutable to `i8`.
+unsafe impl super::AtomicType for bool {
+    type Repr = i8;
+}
+
 // SAFETY: `i8` has the same size and alignment with itself, and is round-trip transmutable to
 // itself.
 unsafe impl super::AtomicType for i8 {
-- 
2.51.0